DC power plane structure

ABSTRACT

A DC power plane structure applied in multi-layer circuit board is provided. The DC power plane structure includes a first circuit area for receiving a DC power, a noise filter with one end electrically connected to a DC power output end of the first circuit area, and a second circuit area which is electrically isolated from the first circuit area. The second circuit area has a band gap structure, and the DC power input end of the band gap structure is electrically connected to the other end of the noise filter for inhibiting high-frequency noise generated between layers of the multi-layer circuit board.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a direct current (DC) power planestructure, and more particularly to a DC power plane structure forinhibiting noise between layers of a multi-layer circuit board.

2. Related Art

Recently, as the mass are increasingly demanding for higher informationtransmission speed, the frequency of signal transmission becomes higherand higher. Thus, a high-frequency digital circuit design becomes a maindevelopment field of circuit design towards higher speed, compactedvolume, and low voltage. Due to the demand for a design with smallvolume, multi-layer printed circuit boards have been widely applied inthe circuit design. However, as the signal transmission frequencybecomes higher, noise is generated between a power plane and a groundplane in the multi-layer printed circuit board, which negatively affectsthe signal transmission quality. Accordingly, how to inhibit noisetransmitted along with signals has become an important subject inhigh-frequency digital circuit design.

In a high-frequency digital circuit, when a signal line is connected toa power plane, parasitic inductance, capacitance, and resistance effectsoccurs between the layers of the multi-layer printed circuit board. Whenquickly switching signals of an integrated circuit (IC) in thehigh-frequency digital circuit, a transient voltage difference isgenerated in the power plane, thus causing noise. The noises are furtherpropagated to other positions in the circuit in the form of parallelplate waveguide, which are one of the major noise sources in digitalsystem.

However, some common methods of inhibiting wideband noises have beendisclosed in prior arts, in which capacitance walls, capacitors with ahigh capacitance are arranged and power planes are partitioned toinhibit the noise. In the design of arranging capacitors, decouplingcapacitors are arranged around a noise source to provide a noise groundpath. Generally, the more the capacitors are arranged around the noisesource, the better the effect of noise inhibition is. However, in theabove designs, resonance noises of certain frequencies still exist,which cause inconvenience in the layout of wirings on the circuit board.Thus, the manufacturing cost is greatly increased, and the concept ofshort, small, light, and thin design cannot be achieved.

Also, referring to FIGS. 1 and 2, an exploded structural view of amulti-layer circuit board and a top view of a power plane in the priorart are shown. As shown in FIGS. 1 and 2, the method of inhibiting thewideband noise by partitioning a power plane 10 is provided, in whichthe power plane 10 is partitioned into a first circuit area 11 and asecond circuit area 12 with a slit there between. The first circuit area11 has an component or IC that is tendered to be interfered by the noiseto generate a resonance, and the second circuit area has an input/outputport (I/O port) 14. Thus, the slit has a function of isolating thenoise. The two areas are electrically connected with each other only bya noise filter 13 to let signals pass through and filter a part ofnoise. The noise filter 13 is a ferrite bead which is a ferromagneticmaterial. The ferrite bead can increasingly generate higher impedance asthe frequency goes up, and a ferrite material may react with a magneticfield resulting from the circuit, resulting in a loss. Different ferritematerials and geometrical structures may cause an attenuation effect todifferent frequencies.

The method described above can overcome the problem of high cost due toemploying the capacitance wall. However, the partitioned power plane 10may result in a high-frequency resonance between the power plane 10 anda ground plane 20. The noise filter 13 can only filter noise with lowfrequency and cannot reduce the high-frequency noise, and thushigh-frequency noise is transmitted with signals via the transmissionline. This is a difficult problem in the prior art.

Nowadays, high-frequency signal transmission becomes a main trend forsignal transmission, and the high-frequency noise will interfere withhigh-frequency signals, resulting in a distortion of the high-frequencysignals. Therefore, it is an important subject for the design ofhigh-frequency digital circuit to effectively inhibit the high-frequencynoise transmitted on the power plane 10.

SUMMARY OF THE INVENTION

In view of the above problems, it is a main object of the presentinvention to provide a power plane structure for inhibitinghigh-frequency noise, so as to solve the problems existing in the priorart that the method of partitioning the power plane can only inhibitlow-frequency noise other than the high-frequency noise as the resonanceof high-frequency noise is caused. And the high manufacturing costcaused by the use of a large number of capacitors in the conventionalart can be reduced, also solving the problem of difficult wiring layoutand complicated manufacturing processes.

In order to achieve the above object, the present invention provides aDC power plane structure arranged in a multi-layer circuit board. The DCpower plane structure includes a first circuit area for inputting a DCpower, a noise filter with one end electrically connected to a DC poweroutput end of the first circuit area, and a second circuit area which iselectrically isolated from the first circuit area. The second circuitarea is formed with a band gap structure, and the DC power input end ofthe band gap structure is electrically connected to the other end of thenoise filter. According to the present invention, the band gap structurecan also be formed in the first circuit area, and one end of the noisefilter is electrically connected to the DC power output end of the bandgap structure, and the DC power input end of the second circuit area iselectrically connected to the other end of the noise filter.

The efficacy of the present invention is to provide a DC power planestructure, which adopts the technique of partitioning the power planeand meanwhile forming an electromagnetic band gap (EBG) or photonic bandgap (PBG) structure on the power plane, so that both the low-frequencyand high-frequency noise can be inhibited at the same time, therebygreatly improving the signal transmission quality. Also, the abovedesign does not need to use a large number of capacitors or arrangecapacitors with a high capacitance, thus reducing the manufacturingcost, simplifying the manufacturing processes of the circuit boardstructure, and achieving the short, small, light, and thin design.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given herein below for illustration only, and thusare not limitative of the present invention, and wherein:

FIG. 1 is an exploded structural view of a multi-layer circuit board inthe prior art;

FIG. 2 is a top view of a power plane in the prior art;

FIG. 3 is a top view of the first embodiment of the present invention;

FIG. 4 is a top view of the second embodiment of the present invention;

FIG. 5 is a top view of the third embodiment of the present invention;and

FIG. 6 shows the relationship between frequencies and noise signalintensity.

DETAILED DESCRIPTION OF THE INVENTION

The purpose, construction, characteristics, and functions of the presentinvention are further described accompanied with the embodiments below.

First, referring to FIG. 3, a top view of the first embodiment of thepresent invention is shown. As shown in FIG. 3, a power plane 110 has aDC power 30, and an I/O port 114 for connecting a transmission line sothat the power plane 110 is connected with another circuit board totransmit or receive a signal. The power plane 110 is partitioned intotwo parts, namely a first circuit area 111 and a second circuit area 112which are electrically connected through a noise filter 113, and a bandgap structure 116 is formed on the second circuit area 112.

A band gap structure 116, for example, an electromagnetic band gap (EBG)structure or a photonic band gap (PBG) structure is formed on the secondcircuit area 112, so as to make one end of the noise filter 113electrically connected to the DC power output end of the first circuitarea 111. Also, the second circuit area 112 is electrically isolatedfrom the first circuit area 111, and the DC power input end of the bandgap structure 116 is electrically connected to the other end of thenoise filter 113, so as to inhibit the transmission of low-frequencynoise, thereby achieving the filtering effect. The main function of theband gap structure 116 in the present invention is to inhibit thehigh-frequency noise propagating on the power plane 110. As shown inFIG. 3, the band gap structure 116 has, for example, thin-wire channelstructures 1161, thin slit structures 1162, and units 1163, and each ofthem has a function of inhibiting noise. The thin-wire channelstructures 1161 mainly function to provide an equivalent inductance. Thethin-wire channel structures 1161 refer to connecting structures betweenany two units 1163 or connecting structures between one of the units1163 and the second circuit area 112. The thin slit structure 1162mainly functions to provide an equivalent inductance. The thin slitstructures 1162 refer to slits between the units 1163 and the thin-wirechannel structures 1161 and slits between the units 1163 and the secondcircuit area 112. Thus, the above band gap structure 116 is anequivalent circuit connected in parallel with a plurality of capacitorsand inductors, through which a great number of noise ground paths can beprovided to achieve the purpose of filtering and inhibitinghigh-frequency. noise, thereby solving the problems existing in theprior art.

Furthermore, referring to FIG. 4, a top view of the second embodiment ofthe present invention is provided. As shown in FIG. 4, the secondembodiment of the present invention is substantially the same as thefirst embodiment in terms of main structures, and only the difference isdescribed herein. The band gap structure 116 is formed on the firstcircuit area 111 in the second embodiment so that one end of the noisefilter 113 is electrically connected to the DC power output end of theband gap structure 116, the second circuit area 112 is electricallyisolated from the first circuit area 111, and the DC power input end ofthe second circuit area 112 is electrically connected to the other endof the noise filter 113. The filtering effect of the second embodimentis the same as that described in the first embodiment, thereby achievingthe function of inhibiting the high-frequency noise. The embodiments ofthe present invention are not limited to the first and secondembodiments. According to the present invention, the band gap structure116 can also be formed both on the second circuit area 112 and on thefirst circuit area 111, and other parts are the same as those describedin the first and second embodiments, and thus the effect of inhibitingnoise can be further improved.

Besides, referring to FIG. 5, a top view of the third embodiment of thepresent invention is provided. As shown in FIG. 5, the third embodimentof the present invention is similar to the first embodiment in terms ofmain structures, and only the difference is that there is no noisefilter between the first circuit area 111 and the second area 112.Therefore, in the third embodiment, one more limitation is that thefirst circuit area 111 and the second area 112 should respectivelypossess different electric potential. Then the filtering effect of thethird embodiment with the band gap structure 116 on the first circuitarea 111 or the second area 112 is also effective as that described inthe first or the second embodiment, thereby achieving the function ofinhibiting the high-frequency noise.

The relationship between frequencies and noise signal intensity is shownin FIG. 6, in order to illustrate the effect of solving the problem ofthe interference caused by wideband noise between layers of amulti-layer circuit board, which effectively inhibits the transmissionof noise. As shown in FIG. 6, a distribution curve 101 denotes therelationship between frequencies and noise signal intensity when thepower plane 110 has not partitioned in two parts and the band gapstructure 116 is not formed. A distribution curve 102 denotes therelationship between frequencies and noise signal intensity when thepower plane 110 is partitioned into the first circuit area 111 and thesecond circuit area 112 but the band gap structure 116 is not formed,for example, the power plane 10 structure as shown in FIG. 2. Adistribution curve 103 denotes the relationship between frequencies andnoise signal intensity when the power plane 110 is partitioned into thefirst circuit area 111 and the second circuit area 112 and the band gapstructure 116 is formed on at least one circuit areas, for example, thepower plane 110 structure shown in FIG. 3 to 5. The distribution curves101, 102 and 103 are obtained from the calculation and simulation byusing simulation software Zeland IE3D.

Moreover, by comparing the distribution curve 101 with the distributioncurve 102, it can be seen that the noise signal intensity with thefrequency below 4 GHz in the distribution curve 102 is about 20 dB lowerthan the noise signal intensity in the distribution curve 101. However,the signal intensity with the frequency above 4 GHz in the distributioncurve 102 is only 5 to 10 dB lower than the noise signal intensity inthe distribution curve 101. Thus, it can be seen that the partitionedstructures of power plane 10 in the prior art as shown in FIG. 2 cansignificantly inhibit low-frequency noise but cannot effectively inhibithigh-frequency noise propagating on the power plane 10.

Comparing the distribution curve 102 with the distribution curve 103, itcan be seen that the noise signal intensity with the frequency above 4GHz in the distribution curve 103 greatly decreases as compared with thenoise signal intensity in the distribution curve 102. And the noisesignal intensity with the frequency between 4 GHz to 8 GHz is decreasedabout 22 dB, while the noise signal intensity with the frequency between4 GHz to 6.5 GHz is even decreased about 28 dB. That is, thedistribution curve 103 indicates that the band gap structure 116 formedon the power plane 110 structure in the present invention has a greateffect of inhibiting high-frequency noise. However, when comparing thedistribution curve 103 with the distribution curve 102 at the frequencybelow 4 GHz, the noise signal intensity does not decrease significantly.Thus, it can be seen that the band gap structure 116 formed on the powerplane 110 structure in the present invention does not have the effect ofinhibiting the noise with the frequency below 4 GHz.

Therefore, the present invention provides a DC power plane structureapplied in the multi-layer circuit board, in which the technique ofpartitioning the power plane 110 for effectively inhibitinglow-frequency noise with the frequency below 4 GHz and the technique offorming a band gap structure 116 on the first circuit area or the secondcircuit area for effectively inhibiting the transmission ofhigh-frequency noise, especially those with the frequency between 4 GHzto 8 GHz are used together.

The present invention can solve the problem existing in the prior arts.That is, the technique of partitioning the power plane 10 cannot be usedto effectively inhibit high-frequency noise only, so that thehigh-frequency noise will be easily transmitted to the I/O port and thenoutput via the transmission line, thereby affecting the transmissionquality of the high-frequency signal. Therefore, by partitioning thepower plane 110 and meanwhile forming the band gap structure 116 on thepower plane 110, the present invention can inhibit both low-frequencyand high-frequency noise signals so as to greatly improve the signaltransmission quality. Furthermore, the above-mentioned design does notneed to use a large number of capacitors or arrange capacitors with highcapacitance, thus reducing the manufacturing cost, simplifying themanufacturing processes of the circuit board, and achieving a short,small, light and thin design.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A direct current (DC) power plane structure applied in a multi-layercircuit board, comprising: a first circuit area for receiving a DCpower; and a second circuit area which is electrically isolated from thefirst circuit area, wherein the second circuit area is formed with aband gap structure.
 2. The DC power plane structure of claim 1, thedirect current power plane structure further comprises a noise filterwith one end being electrically connected to a DC power output end ofthe first circuit area and the other end of the noise filter iselectrically connected to the DC power input end of the band gapstructure.
 3. The DC power plane structure of claim 1, wherein thesecond circuit area has an I/O (Input/Output) port used for connecting atransmission line such that the second circuit area is connected toanother circuit board to transmit or receive a signal.
 4. The DC powerplane structure of claim 1, wherein the band gap structure comprises: aplurality of units; a plurality of thin-wire channel structures,connected between any two of the units and between the units and thesecond circuit area, so as to serve as a plurality of inductors for theband gap structure; and a plurality of thin slit structures, disposedbetween the units and the thin-wire channel structures and between theunits and the second circuit area so as to serve as a plurality ofcapacitors for the band gap structure, and connected in series with thethin-wire channel structures to form a plurality of noise ground paths.5. The DC power plane structure of claim 2, wherein the noise filter isa ferrite bead.
 6. The DC power plane structure of claim 1, wherein theband gap structure is an electromagnetic band gap (EBG) structure. 7.The DC power plane structure of claim 1, wherein the band gap structureis a photonic band gap (PBG) structure.
 8. A direct current (DC) powerplane structure applied in a multi-layer circuit board, comprising: afirst circuit area for receiving a DC power, the first circuit areabeing formed with a band gap structure; and a second circuit areaelectrically isolated from the first circuit area.
 9. The DC power planestructure of claim 8, the direct current power plane structure furthercomprises a noise filter with one end being electrically connected to aDC power output end of the band gap structure, and the other end of thenoise filter is electrically connected to the DC power input end of thesecond circuit area.
 10. The DC power plane structure of claim 8,wherein the second circuit area has an I/O port for connecting atransmission line such that the second circuit area is connected toanother circuit board to transmit or receive a signal.
 11. The DC powerplane structure of claim 8, wherein the band gap structure comprises: aplurality of units; a plurality of thin-wire channel structures,connected between any two of the units and between the units and thefirst circuit area, so as to serve as a plurality of inductors for theband gap structure; and a plurality of thin slit structures, disposedbetween the units and the thin-wire channel structures and between theunits and the first circuit area so as to serve as a plurality ofcapacitors for the band gap structure, and connected in series with thethin-wire channel structures so as to form a plurality of noise groundpaths.
 12. The DC power plane structure of claim 9, wherein the noisefilter is a ferrite bead.
 13. The DC power plane structure of claim 8,wherein the band gap structure is an electromagnetic band gap (EBG)structure.
 14. The DC power plane structure of claim 8, wherein the bandgap structure is a photonic band gap (PBG) structure.